It is known in the art that zeolitic aluminosilicates (hereinafter "zeolites") have adsorptive properties and that the apparent pore size of zeolites may be modified by the level of hydration of the zeolites. For example, the change in the apparent pore size of an amine modified chabazite is disclosed in U.S. Pat. No. 2,930,447. U.S. Pat. No. 1,813,174 disclosed the selectivity of chabazite for oxygen over hydrogen as a function of the degree of dehydration. Similarly, a 1936 publication, Lamb and Woodhouse (J.A.C.S. 58,2637) describes the adsorptive behavior of chabazite during progressive dehydration.
Methods for the modification of zeolites to enhance their selectivity and/or adsorptive capacity have been disclosed. U.S. Pat. No. 3,224,167 discloses a process for reducing the apparent pore size of sodium A zeolite by using a steaming procedure whereby the oxygen adsorption capacity of a reactivated zeolite has been reduced. One of the particular drying problems noted in U.S. Pat. No. 3,224,167 related to the drying of monochlorodifluoromethane. Under some conditions the monochlorodifluoromethane was observed to decompose and zeolite A was observed to lose some of its capacity to adsorb water. The steaming process of the sodium zeolite A was disclosed to reduce the apparent pore size of the sodium zeolite A and reduce the decomposition of the sodium zeolite A by decreasing the adsorption of monochlorodifluoromethane by the sodium zeolite A.
The use of chabazite-type zeolites to dry and purify process streams containing acid contaminants has been commercially employed. Adsorbents containing chabazite-type zeolites have been employed for natural gas drying, hydrogen drying in hydrogen recycle streams and drying halogenated hydrocarbon streams. The chabazite-type zeolite adsorbents employed heretofore contained a K.sub.2 O/Al.sub.2 O.sub.3 mole oxide up to about 0.3 for such adsorbents. The use of a chabazite-type zeolite (AW500.TM.; trademark of Union Carbide Corporation, Danbury, CT.) for several gas drying applications is generally disclosed in Oil & Gas Journal, J. J. Collins, Dec. 2, 1963.